The present invention concerns a process for extracting natural liquor from ligneous plant matter, a device allowing implementation of the process and use of the process for the production of dried ligneous plants, or liquor.
By the term xe2x80x9csaw woodxe2x80x9d is understood wood stemming directly from initial processing (sawing).
There is known from patent application WO 82/01766 a process for drying wood, using microwaves at a frequency of 915 MHz applied to the elements of wood to be dried in order to raise their internal temperature and to make them reject water. Water rejected in this way is evaporated on the surface of the wood by low speed air circulation obtained by fans. The air with about 80% humidity passes over condensers in order to extract this humidity.
In the document WO 82/01411, the same principle is used but in the latter, it is additionally noted that the air temperature must always be lower than the internal temperature of the wood. This document cites as a drawback the fact that the surface area of the material is heated with microwaves before the internal part of the material is heated. In this document, it is therefore proposed to control the process of converting electromagnetic energy into heat energy in order to concentrate the waves on the water in the material. Moreover, it is suggested to act on the climate within the chamber by maintaining a high enough percentage of air humidity for the surface of the product not to dry out before the humidity at the wood core is extracted. To this end, during the initial phase of the drying process, water in an atomised form is introduced into the chamber to maintain a high moisture content.
Likewise, the article which appeared in the review xe2x80x9cHolz als roh und werkstoffxe2x80x9d in 1995, pp 333 to 338, published by Springer-Verlag and entitled xe2x80x9cMicrowave drying of pine and sprucexe2x80x9d by A. L. ANTTI gives instructions on drying wood with microwaves operating at frequencies of 915 or 2450 MHz and a power density located in the range of 25 to 78 kW/m3 to reach the internal temperature of the wood at about 140xc2x0 C. and to achieve a vapour pressure internal to the wood of 25 KPa. The internal pressure realised in this way is very high to allow very rapid drain-off of water. The drawback of the process is that fractures develop in the fibres. The drying process begins by rapid microwave drying at about 70xc2x0 C. then an intermittent exposure to microwaves during the drying and lastly, a drying operation by controlling the temperature of the wood beneath fibre saturation keeping within a maximum temperature of 110xc2x0 C.
In every hypothetical case, it is clear that air is used as the vehicle to remove the humidity discharged by the wood. For these reasons, the air moisture content must remain below the air saturation value in water vapour. It is therefore necessary in known devices for the air to be dehumidified in order to be able to dry out the wood. Moreover, it is necessary to have an air temperature below that of the wood in order to allow evaporation. The drawback of all these devices is that big energy losses are generated and energy consumption is not optimised. Indeed the higher the wood temperatures are to be, the more the power of the microwave generators must be proportionate and the higher their cost given drying operations lasting several hours, the greater the energy consumed. Indeed, it may be seen in the article cited above that drying times are between 3 and 5 hours according to the thickness of the wood and the power of the equipment. Moreover, none of the known processes manages to get below 30% humidity in the wood after drying.
Lastly it is also known from French patent applications 2 763 795 and 2 705 035 for a natural product to be extracted by microwaves from a biological material by making the biological material undergo, in the absence of any solvent, microwave irradiation in order to cause at least a part of the water contained in the material to evaporate and the cellular structures to burst. The process consists in applying reduced pressure intermittently within the enclosure in order to facilitate this bursting. The use of microwaves serves essentially to compensate for the drop in temperature resulting from the water evaporation. Whatever the circumstances, the temperatures used remain below 100xc2x0 C. and the pressures below atmospheric pressure (1 bar). According to this process, pressures of about 100 millibars and temperatures of about 70xc2x0 C. are used.
The purpose of the present invention is to propose a process, which allows energy to be optimised and a maximum yield in liquor production, per quantity of processed fibrous plant matter, to be obtained.
This purpose is fulfilled by the fact that the process for extracting natural liquor from ligneous plant matter comprises:
a stage of pressurisation above atmospheric pressure of a sealed enclosure containing the matter;
a stage of creation or injection of saturated water vapour;
a stage of heating to the core of the plant matter by electromagnetic waves;
a stage of gravitory recovery of the liquid exudations emerging from the processed plant matter.
According to another particularity, the recovery stage may be executed at least in part during the stage of creation or injection of saturated water vapour.
According to another particularity, the total pressure is between 1.5 and 9.6 bars.
According to another particularity, the total pressure is adapted as a function of the plant matter processed and of the vapour temperature surrounding this matter.
According to another particularity, the wave power is modulated to allow the matter to be heated to the core, which is from a few tenths of a degree to a few degrees above the vapour temperature resulting from the total pressure selected.
According to another particularity the volume of water at atmospheric pressure and external ambient temperature is equivalent to two to four times the volume of air contained in the enclosure in the same conditions.
According to another particularity, the volume necessary for the saturated vapour pressure, for the operational temperature selected is about three times the air mass contained in the enclosure at ambient temperature.
According to another particularity, the wave frequency is adapted to the size of the mass of plant matter to be processed in the enclosure, so as to allow the waves to penetrate right to the core of the plant mass to be processed.
According to another particularity, the wave frequency is between 13 MHz and 2450 MHz.
According to another particularity, the process comprises a stage of draining off the liquors out of the enclosure under pressure during or in the course of the extraction process.
According to another particularity, the process comprises a stage of adaptation, after the liquors have been drained off, of the conditions of total pressure, temperature and wave control power to facilitate the penetration into the wood of additive products injected into the enclosure.
Another purpose of the invention is to propose a device allowing the process to be implemented.
This purpose is fulfilled by the fact that the device is constituted by a sealed enclosure resistant to pressure, by a plurality of windows made of quartz or of any other material suiting waves with an electromagnetic wave generator placed near each window, so as to emit the waves transversely to the mass of plant material placed in the enclosure, a device for generating saturated water vapour at pressure above atmospheric pressure so as to create or inject a saturated water vapour pressure at a vapour temperature and at a total pressure determined as a function of the plant to be processed.
According to another particularity, the device comprises pressurised air circulation means.
According to another particularity, the vapour generator device allows vapour to be injected under pressure at the pre-set vapour temperature and total pressure.
According to another particularity, the vapour generator device comprises in the enclosure a receptacle for receiving a quantity of water corresponding to two to four times the air mass contained in the enclosure at external ambient temperature and means of heating this water to bring it to the vapour state.
According to another particularity, the heating means are controlled by a device, which measures the total pressure prevailing within the enclosure allowing the water heating to be interrupted when the desired pressure is reached.
According to another particularity, the enclosure comprises a device for recovering liquors by run-off and/or gravity of the liquor extracted from the matter.
According to another particularity, the liquor recovery device communicates via a sluice with the outside of the enclosure, said sluice being controlled in order to carry out partial draining of liquor while the machine is operating.
According to another particularity, the mass of plant matter processed in a liquor extraction operation is constituted by plant type and the pressure and temperature conditions are determined as a function of the plant oil type in order to extract the worthwhile active constituents in the best conditions.
According to another particularity, the woods are processed with bark or without bark straight from felling.
According to another particularity, the plants are the branches and leaves resulting from pruning.
A final purpose is to obtain a natural liquor.
This purpose is fulfilled by the fact that the natural liquor is obtained from processing ligneous plant matter.
Other particularities and advantages of the present invention will emerge more clearly from reading the following description given with reference to the appended drawings in which: